May 23, 2012
Courtesy of Washington State University
and World
Science staff

Sci­en­tists have found in­creased stress sen­si­ti­vity
and dif­fer­ences in weight gain in rats whose an­ces­tors were ex­posed to a
hor­mone-dis­rupt­ing chem­i­cal three genera­t­ions ear­li­er.

The re­search­ers ex­posed preg­nant rats to vin­clo­zolin, a pop­u­lar fruit and veg­e­ta­ble fun­gi­cide known to dis­rupt hor­mones. They then put the ro­dents’ great-grandpups through var­i­ous tests and found them more anx­ious, stress-sen­si­tive
and prone to great­er ac­ti­vity in stress-related brain ar­eas than un­ex­posed rats’ de­scen­dants.

Sci­en­tists have found in­creased stress sen­si­ti­vity and dif­fer­ences in weight gain in rats whose an­ces­tors were ex­posed to a chem­i­cal in their en­vi­ron­ment three genera­t­ions ear­li­er.

“We are now in the third hu­man genera­t­ion since the start of the chem­i­cal rev­o­lu­tion, since hu­mans have been ex­posed to these kinds of tox­ins,” said Da­vid Crews of the Uni­vers­ity of Tex­as at Aus­tin, one of the in­ves­ti­ga­tors. “This is the an­i­mal mod­el of that.”

The dif­fer­ences in weight gain seen in the study were in­tri­guing but re­quire fur­ther stu­dy, he added.

It seems clear that “the an­ces­tral ex­po­sure of your great grand­moth­er al­ters your brain de­vel­op­ment to then re­spond to stress dif­fer­ent­ly,” said Mi­chael Skin­ner of Wash­ing­ton State Uni­vers­ity, who worked with Crews. The find­ings are pub­lished in the lat­est is­sue of the jour­nal
Pro­ceed­ings of the Na­t­ional Acad­e­my of Sci­ences.

The re­search­ers had pre­vi­ously found vin­clo­zolin ex­po­sure can ef­fect sub­se­quent genera­t­ions by af­fect­ing how genes are turned on and off, a pro­cess called epi­ge­net­ics. In that case, the ep­i­ge­net­ic in­her­it­ance al­tered how rats choose mates.

The new re­search goes fur­ther.

“How well you so­cial­ize or how your anx­i­e­ty lev­els re­spond to stress may be as much your an­ces­tral ep­i­ge­net­ic in­her­it­ance as your in­di­vid­ual early-life events,” Skin­ner said. This could ex­plain why some peo­ple suf­fer post-traumatic stress syn­drome while oth­ers don’t, he added.

“We have been see­ing real in­creases in men­tal dis­or­ders like au­tism and bi­po­lar dis­or­der,” said Crews. “It’s more than just a change in di­ag­nos­tics. The ques­tion is why? Is it be­cause we are liv­ing in a more frantic world, or be­cause we are liv­ing in a more frantic world and are re­sponding to that in a dif­fer­ent way be­cause we have been ex­posed? I fa­vor the lat­ter.”

Scientists have found increased stress sensitivity and differences in weight gain in rats whose ancestors were exposed to a chemical in their environment three generations earlier.
The researchers exposed pregnant rats to vinclozolin, a popular fruit and vegetable fungicide known to disrupt hormones. They then put the rodents’ great-grandpups through various tests and found them more anxious, more stress-sensitive, and showing greater activity in stress-related brain areas than unexposed rats’ descendants.
“We are now in the third human generation since the start of the chemical revolution, since humans have been exposed to these kinds of toxins,” said David Crews of the University of Texas at Austin, one of the investigators. “This is the animal model of that.”
The differences in weight gain seen in the study were intriguing but require further study, he added.
It seems clear that “the ancestral exposure of your great grandmother alters your brain development to then respond to stress differently,” said Michael Skinner of Washington State University, who worked with Crews. The findings are published in the latest issue of the journal Proceedings of the National Academy of Sciences.
The researchers had previously found vinclozolin exposure can effect subsequent generations by affecting how genes are turned on and off, a process called epigenetics. In that case, the epigenetic inheritance altered how rats choose mates.
The new research goes further.
“How well you socialize or how your anxiety levels respond to stress may be as much your ancestral epigenetic inheritance as your individual early-life events,” Skinner said. This could explain why some people suffer post-traumatic stress syndrome while others don’t, he added.
“We have been seeing real increases in mental disorders like autism and bipolar disorder,” said Crews. “It’s more than just a change in diagnostics. The question is why? Is it because we are living in a more frantic world, or because we are living in a more frantic world and are responding to that in a different way because we have been exposed? I favor the latter.”